diff --git a/services/surfaceflinger/DisplayHardware/DisplaySurface.h b/services/surfaceflinger/DisplayHardware/DisplaySurface.h
index 2eca3cb..b0f460d 100644
--- a/services/surfaceflinger/DisplayHardware/DisplaySurface.h
+++ b/services/surfaceflinger/DisplayHardware/DisplaySurface.h
@@ -32,6 +32,18 @@
 public:
     virtual sp<IGraphicBufferProducer> getIGraphicBufferProducer() const = 0;
 
+    // prepareFrame is called after the composition configuration is known but
+    // before composition takes place. The DisplaySurface can use the
+    // composition type to decide how to manage the flow of buffers between
+    // GLES and HWC for this frame.
+    enum CompositionType {
+        COMPOSITION_UNKNOWN = 0,
+        COMPOSITION_GLES    = 1,
+        COMPOSITION_HWC     = 2,
+        COMPOSITION_MIXED   = COMPOSITION_GLES | COMPOSITION_HWC
+    };
+    virtual status_t prepareFrame(CompositionType compositionType) = 0;
+
     // Should be called when composition rendering is complete for a frame (but
     // eglSwapBuffers hasn't necessarily been called). Required by certain
     // older drivers for synchronization.
diff --git a/services/surfaceflinger/DisplayHardware/FramebufferSurface.cpp b/services/surfaceflinger/DisplayHardware/FramebufferSurface.cpp
index 10bca38..3f51345 100644
--- a/services/surfaceflinger/DisplayHardware/FramebufferSurface.cpp
+++ b/services/surfaceflinger/DisplayHardware/FramebufferSurface.cpp
@@ -72,6 +72,10 @@
     return getBufferQueue();
 }
 
+status_t FramebufferSurface::prepareFrame(CompositionType compositionType) {
+    return NO_ERROR;
+}
+
 status_t FramebufferSurface::advanceFrame() {
     // Once we remove FB HAL support, we can call nextBuffer() from here
     // instead of using onFrameAvailable(). No real benefit, except it'll be
diff --git a/services/surfaceflinger/DisplayHardware/FramebufferSurface.h b/services/surfaceflinger/DisplayHardware/FramebufferSurface.h
index c86e9ae..92a7f9b 100644
--- a/services/surfaceflinger/DisplayHardware/FramebufferSurface.h
+++ b/services/surfaceflinger/DisplayHardware/FramebufferSurface.h
@@ -41,6 +41,7 @@
 
     virtual sp<IGraphicBufferProducer> getIGraphicBufferProducer() const;
 
+    virtual status_t prepareFrame(CompositionType compositionType);
     virtual status_t compositionComplete();
     virtual status_t advanceFrame();
     virtual void onFrameCommitted();
diff --git a/services/surfaceflinger/DisplayHardware/HWComposer.cpp b/services/surfaceflinger/DisplayHardware/HWComposer.cpp
index 5082192..ca98133 100644
--- a/services/surfaceflinger/DisplayHardware/HWComposer.cpp
+++ b/services/surfaceflinger/DisplayHardware/HWComposer.cpp
@@ -16,9 +16,6 @@
 
 #define ATRACE_TAG ATRACE_TAG_GRAPHICS
 
-// Uncomment this to remove support for HWC_DEVICE_API_VERSION_0_3 and older
-#define HWC_REMOVE_DEPRECATED_VERSIONS 1
-
 #include <stdint.h>
 #include <stdio.h>
 #include <stdlib.h>
@@ -50,9 +47,9 @@
 
 namespace android {
 
-// This is not a real HWC version. It's used for in-development features that
-// haven't been committed to a specific real HWC version.
-#define HWC_DEVICE_API_VERSION_1_EXP HARDWARE_DEVICE_API_VERSION_2(1, 0xFF, HWC_HEADER_VERSION)
+#ifndef HWC_DEVICE_API_VERSION_1_3
+#define HWC_DEVICE_API_VERSION_1_3 HARDWARE_DEVICE_API_VERSION_2(1, 3, HWC_HEADER_VERSION)
+#endif
 
 #define MIN_HWC_HEADER_VERSION HWC_HEADER_VERSION
 
@@ -156,8 +153,8 @@
 
         // the number of displays we actually have depends on the
         // hw composer version
-        if (hwcHasApiVersion(mHwc, HWC_DEVICE_API_VERSION_1_EXP)) {
-            // 1.?? adds support for virtual displays
+        if (hwcHasApiVersion(mHwc, HWC_DEVICE_API_VERSION_1_3)) {
+            // 1.3 adds support for virtual displays
             mNumDisplays = MAX_DISPLAYS;
         } else if (hwcHasApiVersion(mHwc, HWC_DEVICE_API_VERSION_1_1)) {
             // 1.1 adds support for multiple displays
@@ -582,7 +579,7 @@
         }
         mLists[i] = disp.list;
         if (mLists[i]) {
-            if (hwcHasApiVersion(mHwc, HWC_DEVICE_API_VERSION_1_EXP)) {
+            if (hwcHasApiVersion(mHwc, HWC_DEVICE_API_VERSION_1_3)) {
                 mLists[i]->outbuf = NULL;
                 mLists[i]->outbufAcquireFenceFd = -1;
             } else if (hwcHasApiVersion(mHwc, HWC_DEVICE_API_VERSION_1_1)) {
diff --git a/services/surfaceflinger/DisplayHardware/VirtualDisplaySurface.cpp b/services/surfaceflinger/DisplayHardware/VirtualDisplaySurface.cpp
index 2838b23..90bfce7 100644
--- a/services/surfaceflinger/DisplayHardware/VirtualDisplaySurface.cpp
+++ b/services/surfaceflinger/DisplayHardware/VirtualDisplaySurface.cpp
@@ -14,27 +14,89 @@
  * limitations under the License.
  */
 
+// #define LOG_NDEBUG 0
 #include "VirtualDisplaySurface.h"
-
-#include <cutils/log.h>
-#include <gui/IGraphicBufferProducer.h>
+#include "HWComposer.h"
 
 // ---------------------------------------------------------------------------
 namespace android {
 // ---------------------------------------------------------------------------
 
+#define VDS_LOGE(msg, ...) ALOGE("[%s] "msg, \
+        mDisplayName.string(), ##__VA_ARGS__)
+#define VDS_LOGW_IF(cond, msg, ...) ALOGW_IF(cond, "[%s] "msg, \
+        mDisplayName.string(), ##__VA_ARGS__)
+#define VDS_LOGV(msg, ...) ALOGV("[%s] "msg, \
+        mDisplayName.string(), ##__VA_ARGS__)
+
+static const char* dbgCompositionTypeStr(DisplaySurface::CompositionType type) {
+    switch (type) {
+        case DisplaySurface::COMPOSITION_UNKNOWN: return "UNKNOWN";
+        case DisplaySurface::COMPOSITION_GLES:    return "GLES";
+        case DisplaySurface::COMPOSITION_HWC:     return "HWC";
+        case DisplaySurface::COMPOSITION_MIXED:   return "MIXED";
+        default:                                  return "<INVALID>";
+    }
+}
+
 VirtualDisplaySurface::VirtualDisplaySurface(HWComposer& hwc, int32_t dispId,
         const sp<IGraphicBufferProducer>& sink, const String8& name)
-:   mSink(sink)
+:   ConsumerBase(new BufferQueue(true)),
+    mHwc(hwc),
+    mDisplayId(dispId),
+    mDisplayName(name),
+    mProducerUsage(GRALLOC_USAGE_HW_COMPOSER),
+    mProducerSlotSource(0),
+    mDbgState(DBG_STATE_IDLE),
+    mDbgLastCompositionType(COMPOSITION_UNKNOWN)
 {
-    LOG_ALWAYS_FATAL_IF(dispId >= 0);
+    mSource[SOURCE_SINK] = sink;
+    mSource[SOURCE_SCRATCH] = mBufferQueue;
+
+    resetPerFrameState();
+
+    int sinkWidth, sinkHeight;
+    mSource[SOURCE_SINK]->query(NATIVE_WINDOW_WIDTH, &sinkWidth);
+    mSource[SOURCE_SINK]->query(NATIVE_WINDOW_HEIGHT, &sinkHeight);
+
+    ConsumerBase::mName = String8::format("VDS: %s", mDisplayName.string());
+    mBufferQueue->setConsumerName(ConsumerBase::mName);
+    mBufferQueue->setConsumerUsageBits(GRALLOC_USAGE_HW_COMPOSER);
+    mBufferQueue->setDefaultBufferSize(sinkWidth, sinkHeight);
+    mBufferQueue->setDefaultMaxBufferCount(2);
 }
 
 VirtualDisplaySurface::~VirtualDisplaySurface() {
 }
 
 sp<IGraphicBufferProducer> VirtualDisplaySurface::getIGraphicBufferProducer() const {
-    return mSink;
+    if (mDisplayId >= 0) {
+        return static_cast<IGraphicBufferProducer*>(
+                const_cast<VirtualDisplaySurface*>(this));
+    } else {
+        // There won't be any interaction with HWC for this virtual display,
+        // so the GLES driver can pass buffers directly to the sink.
+        return mSource[SOURCE_SINK];
+    }
+}
+
+status_t VirtualDisplaySurface::prepareFrame(CompositionType compositionType) {
+    if (mDisplayId < 0)
+        return NO_ERROR;
+
+    VDS_LOGW_IF(mDbgState != DBG_STATE_IDLE,
+            "Unexpected prepareFrame() in %s state", dbgStateStr());
+    mDbgState = DBG_STATE_PREPARED;
+
+    mCompositionType = compositionType;
+
+    if (mCompositionType != mDbgLastCompositionType) {
+        VDS_LOGV("prepareFrame: composition type changed to %s",
+                dbgCompositionTypeStr(mCompositionType));
+        mDbgLastCompositionType = mCompositionType;
+    }
+
+    return NO_ERROR;
 }
 
 status_t VirtualDisplaySurface::compositionComplete() {
@@ -42,15 +104,319 @@
 }
 
 status_t VirtualDisplaySurface::advanceFrame() {
-    return NO_ERROR;
+    if (mDisplayId < 0)
+        return NO_ERROR;
+
+    if (mCompositionType == COMPOSITION_HWC) {
+        VDS_LOGW_IF(mDbgState != DBG_STATE_PREPARED,
+                "Unexpected advanceFrame() in %s state on HWC frame",
+                dbgStateStr());
+    } else {
+        VDS_LOGW_IF(mDbgState != DBG_STATE_GLES_DONE,
+                "Unexpected advanceFrame() in %s state on GLES/MIXED frame",
+                dbgStateStr());
+    }
+    mDbgState = DBG_STATE_HWC;
+
+    status_t result;
+    sp<Fence> outFence;
+    if (mCompositionType != COMPOSITION_GLES) {
+        // Dequeue an output buffer from the sink
+        uint32_t transformHint, numPendingBuffers;
+        mQueueBufferOutput.deflate(&mSinkBufferWidth, &mSinkBufferHeight,
+                &transformHint, &numPendingBuffers);
+        int sslot;
+        result = dequeueBuffer(SOURCE_SINK, 0, &sslot, &outFence);
+        if (result < 0)
+            return result;
+        mOutputProducerSlot = mapSource2ProducerSlot(SOURCE_SINK, sslot);
+    }
+
+    if (mCompositionType == COMPOSITION_HWC) {
+        // We just dequeued the output buffer, use it for FB as well
+        mFbProducerSlot = mOutputProducerSlot;
+        mFbFence = outFence;
+    } else if (mCompositionType == COMPOSITION_GLES) {
+        mOutputProducerSlot = mFbProducerSlot;
+        outFence = mFbFence;
+    } else {
+        // mFbFence and mFbProducerSlot were set in queueBuffer,
+        // and mOutputProducerSlot and outFence were set above when dequeueing
+        // the sink buffer.
+    }
+
+    if (mFbProducerSlot < 0 || mOutputProducerSlot < 0) {
+        // Last chance bailout if something bad happened earlier. For example,
+        // in a GLES configuration, if the sink disappears then dequeueBuffer
+        // will fail, the GLES driver won't queue a buffer, but SurfaceFlinger
+        // will soldier on. So we end up here without a buffer. There should
+        // be lots of scary messages in the log just before this.
+        VDS_LOGE("advanceFrame: no buffer, bailing out");
+        return NO_MEMORY;
+    }
+
+    sp<GraphicBuffer> fbBuffer = mProducerBuffers[mFbProducerSlot];
+    sp<GraphicBuffer> outBuffer = mProducerBuffers[mOutputProducerSlot];
+    VDS_LOGV("advanceFrame: fb=%d(%p) out=%d(%p)",
+            mFbProducerSlot, fbBuffer.get(),
+            mOutputProducerSlot, outBuffer.get());
+
+    result = mHwc.fbPost(mDisplayId, mFbFence, fbBuffer);
+    if (result == NO_ERROR) {
+        result = mHwc.setOutputBuffer(mDisplayId, outFence, outBuffer);
+    }
+
+    return result;
 }
 
 void VirtualDisplaySurface::onFrameCommitted() {
+    if (mDisplayId < 0)
+        return;
+
+    VDS_LOGW_IF(mDbgState != DBG_STATE_HWC,
+            "Unexpected onFrameCommitted() in %s state", dbgStateStr());
+    mDbgState = DBG_STATE_IDLE;
+
+    sp<Fence> fbFence = mHwc.getAndResetReleaseFence(mDisplayId);
+    if (mCompositionType == COMPOSITION_MIXED && mFbProducerSlot >= 0) {
+        // release the scratch buffer back to the pool
+        Mutex::Autolock lock(mMutex);
+        int sslot = mapProducer2SourceSlot(SOURCE_SCRATCH, mFbProducerSlot);
+        VDS_LOGV("onFrameCommitted: release scratch sslot=%d", sslot);
+        addReleaseFenceLocked(sslot, mProducerBuffers[mFbProducerSlot], fbFence);
+        releaseBufferLocked(sslot, mProducerBuffers[mFbProducerSlot],
+                EGL_NO_DISPLAY, EGL_NO_SYNC_KHR);
+    }
+
+    if (mOutputProducerSlot >= 0) {
+        int sslot = mapProducer2SourceSlot(SOURCE_SINK, mOutputProducerSlot);
+        QueueBufferOutput qbo;
+        sp<Fence> outFence = mHwc.getLastRetireFence(mDisplayId);
+        VDS_LOGV("onFrameCommitted: queue sink sslot=%d", sslot);
+        status_t result = mSource[SOURCE_SINK]->queueBuffer(sslot,
+                QueueBufferInput(systemTime(),
+                    Rect(mSinkBufferWidth, mSinkBufferHeight),
+                    NATIVE_WINDOW_SCALING_MODE_FREEZE, 0, outFence),
+                &qbo);
+        if (result == NO_ERROR) {
+            updateQueueBufferOutput(qbo);
+        }
+    }
+
+    resetPerFrameState();
 }
 
 void VirtualDisplaySurface::dump(String8& result) const {
 }
 
+status_t VirtualDisplaySurface::requestBuffer(int pslot,
+        sp<GraphicBuffer>* outBuf) {
+    VDS_LOGW_IF(mDbgState != DBG_STATE_GLES,
+            "Unexpected requestBuffer pslot=%d in %s state",
+            pslot, dbgStateStr());
+
+    *outBuf = mProducerBuffers[pslot];
+    return NO_ERROR;
+}
+
+status_t VirtualDisplaySurface::setBufferCount(int bufferCount) {
+    return mSource[SOURCE_SINK]->setBufferCount(bufferCount);
+}
+
+status_t VirtualDisplaySurface::dequeueBuffer(Source source,
+        uint32_t format, int* sslot, sp<Fence>* fence) {
+    status_t result = mSource[source]->dequeueBuffer(sslot, fence,
+            mSinkBufferWidth, mSinkBufferHeight, format, mProducerUsage);
+    if (result < 0)
+        return result;
+    int pslot = mapSource2ProducerSlot(source, *sslot);
+    VDS_LOGV("dequeueBuffer(%s): sslot=%d pslot=%d result=%d",
+            dbgSourceStr(source), *sslot, pslot, result);
+    uint32_t sourceBit = static_cast<uint32_t>(source) << pslot;
+
+    if ((mProducerSlotSource & (1u << pslot)) != sourceBit) {
+        // This slot was previously dequeued from the other source; must
+        // re-request the buffer.
+        result |= BUFFER_NEEDS_REALLOCATION;
+        mProducerSlotSource &= ~(1u << pslot);
+        mProducerSlotSource |= sourceBit;
+    }
+
+    if (result & RELEASE_ALL_BUFFERS) {
+        for (uint32_t i = 0; i < BufferQueue::NUM_BUFFER_SLOTS; i++) {
+            if ((mProducerSlotSource & (1u << i)) == sourceBit)
+                mProducerBuffers[i].clear();
+        }
+    }
+    if (result & BUFFER_NEEDS_REALLOCATION) {
+        mSource[source]->requestBuffer(*sslot, &mProducerBuffers[pslot]);
+        VDS_LOGV("dequeueBuffer(%s): buffers[%d]=%p",
+                dbgSourceStr(source), pslot, mProducerBuffers[pslot].get());
+    }
+
+    return result;
+}
+
+status_t VirtualDisplaySurface::dequeueBuffer(int* pslot, sp<Fence>* fence,
+        uint32_t w, uint32_t h, uint32_t format, uint32_t usage) {
+    VDS_LOGW_IF(mDbgState != DBG_STATE_PREPARED,
+            "Unexpected dequeueBuffer() in %s state", dbgStateStr());
+    mDbgState = DBG_STATE_GLES;
+
+    VDS_LOGV("dequeueBuffer %dx%d fmt=%d usage=%#x", w, h, format, usage);
+
+    mProducerUsage = usage | GRALLOC_USAGE_HW_COMPOSER;
+    Source source = fbSourceForCompositionType(mCompositionType);
+    if (source == SOURCE_SINK) {
+        mSinkBufferWidth = w;
+        mSinkBufferHeight = h;
+    }
+
+    int sslot;
+    status_t result = dequeueBuffer(source, format, &sslot, fence);
+    if (result >= 0) {
+        *pslot = mapSource2ProducerSlot(source, sslot);
+    }
+    return result;
+}
+
+status_t VirtualDisplaySurface::queueBuffer(int pslot,
+        const QueueBufferInput& input, QueueBufferOutput* output) {
+    VDS_LOGW_IF(mDbgState != DBG_STATE_GLES,
+            "Unexpected queueBuffer(pslot=%d) in %s state", pslot,
+            dbgStateStr());
+    mDbgState = DBG_STATE_GLES_DONE;
+
+    VDS_LOGV("queueBuffer pslot=%d", pslot);
+
+    status_t result;
+    if (mCompositionType == COMPOSITION_MIXED) {
+        // Queue the buffer back into the scratch pool
+        QueueBufferOutput scratchQBO;
+        int sslot = mapProducer2SourceSlot(SOURCE_SCRATCH, pslot);
+        result = mBufferQueue->queueBuffer(sslot, input, &scratchQBO);
+        if (result != NO_ERROR)
+            return result;
+
+        // Now acquire the buffer from the scratch pool -- should be the same
+        // slot and fence as we just queued.
+        Mutex::Autolock lock(mMutex);
+        BufferQueue::BufferItem item;
+        result = acquireBufferLocked(&item);
+        if (result != NO_ERROR)
+            return result;
+        VDS_LOGW_IF(item.mBuf != sslot,
+                "queueBuffer: acquired sslot %d from SCRATCH after queueing sslot %d",
+                item.mBuf, sslot);
+        mFbProducerSlot = mapSource2ProducerSlot(SOURCE_SCRATCH, item.mBuf);
+        mFbFence = mSlots[item.mBuf].mFence;
+
+    } else {
+        LOG_FATAL_IF(mCompositionType != COMPOSITION_GLES,
+                "Unexpected queueBuffer in state %s for compositionType %s",
+                dbgStateStr(), dbgCompositionTypeStr(mCompositionType));
+
+        // Extract the GLES release fence for HWC to acquire
+        int64_t timestamp;
+        Rect crop;
+        int scalingMode;
+        uint32_t transform;
+        input.deflate(&timestamp, &crop, &scalingMode, &transform,
+                &mFbFence);
+
+        mFbProducerSlot = pslot;
+    }
+
+    *output = mQueueBufferOutput;
+    return NO_ERROR;
+}
+
+void VirtualDisplaySurface::cancelBuffer(int pslot, const sp<Fence>& fence) {
+    VDS_LOGW_IF(mDbgState != DBG_STATE_GLES,
+            "Unexpected cancelBuffer(pslot=%d) in %s state", pslot,
+            dbgStateStr());
+    VDS_LOGV("cancelBuffer pslot=%d", pslot);
+    Source source = fbSourceForCompositionType(mCompositionType);
+    return mSource[source]->cancelBuffer(
+            mapProducer2SourceSlot(source, pslot), fence);
+}
+
+int VirtualDisplaySurface::query(int what, int* value) {
+    return mSource[SOURCE_SINK]->query(what, value);
+}
+
+status_t VirtualDisplaySurface::setSynchronousMode(bool enabled) {
+    return mSource[SOURCE_SINK]->setSynchronousMode(enabled);
+}
+
+status_t VirtualDisplaySurface::connect(int api, QueueBufferOutput* output) {
+    QueueBufferOutput qbo;
+    status_t result = mSource[SOURCE_SINK]->connect(api, &qbo);
+    if (result == NO_ERROR) {
+        updateQueueBufferOutput(qbo);
+        *output = mQueueBufferOutput;
+    }
+    return result;
+}
+
+status_t VirtualDisplaySurface::disconnect(int api) {
+    return mSource[SOURCE_SINK]->disconnect(api);
+}
+
+void VirtualDisplaySurface::updateQueueBufferOutput(
+        const QueueBufferOutput& qbo) {
+    uint32_t w, h, transformHint, numPendingBuffers;
+    qbo.deflate(&w, &h, &transformHint, &numPendingBuffers);
+    mQueueBufferOutput.inflate(w, h, 0, numPendingBuffers);
+}
+
+void VirtualDisplaySurface::resetPerFrameState() {
+    mCompositionType = COMPOSITION_UNKNOWN;
+    mSinkBufferWidth = 0;
+    mSinkBufferHeight = 0;
+    mFbFence = Fence::NO_FENCE;
+    mFbProducerSlot = -1;
+    mOutputProducerSlot = -1;
+}
+
+// This slot mapping function is its own inverse, so two copies are unnecessary.
+// Both are kept to make the intent clear where the function is called, and for
+// the (unlikely) chance that we switch to a different mapping function.
+int VirtualDisplaySurface::mapSource2ProducerSlot(Source source, int sslot) {
+    if (source == SOURCE_SCRATCH) {
+        return BufferQueue::NUM_BUFFER_SLOTS - sslot - 1;
+    } else {
+        return sslot;
+    }
+}
+int VirtualDisplaySurface::mapProducer2SourceSlot(Source source, int pslot) {
+    return mapSource2ProducerSlot(source, pslot);
+}
+
+VirtualDisplaySurface::Source
+VirtualDisplaySurface::fbSourceForCompositionType(CompositionType type) {
+    return type == COMPOSITION_MIXED ? SOURCE_SCRATCH : SOURCE_SINK;
+}
+
+const char* VirtualDisplaySurface::dbgStateStr() const {
+    switch (mDbgState) {
+        case DBG_STATE_IDLE:      return "IDLE";
+        case DBG_STATE_PREPARED:  return "PREPARED";
+        case DBG_STATE_GLES:      return "GLES";
+        case DBG_STATE_GLES_DONE: return "GLES_DONE";
+        case DBG_STATE_HWC:       return "HWC";
+        default:                  return "INVALID";
+    }
+}
+
+const char* VirtualDisplaySurface::dbgSourceStr(Source s) {
+    switch (s) {
+        case SOURCE_SINK:    return "SINK";
+        case SOURCE_SCRATCH: return "SCRATCH";
+        default:             return "INVALID";
+    }
+}
+
 // ---------------------------------------------------------------------------
 } // namespace android
 // ---------------------------------------------------------------------------
diff --git a/services/surfaceflinger/DisplayHardware/VirtualDisplaySurface.h b/services/surfaceflinger/DisplayHardware/VirtualDisplaySurface.h
index f321795..2b4cf8f 100644
--- a/services/surfaceflinger/DisplayHardware/VirtualDisplaySurface.h
+++ b/services/surfaceflinger/DisplayHardware/VirtualDisplaySurface.h
@@ -17,6 +17,9 @@
 #ifndef ANDROID_SF_VIRTUAL_DISPLAY_SURFACE_H
 #define ANDROID_SF_VIRTUAL_DISPLAY_SURFACE_H
 
+#include <gui/ConsumerBase.h>
+#include <gui/IGraphicBufferProducer.h>
+
 #include "DisplaySurface.h"
 
 // ---------------------------------------------------------------------------
@@ -25,26 +28,187 @@
 
 class HWComposer;
 
-/* This DisplaySurface implementation is a stub used for developing HWC
- * virtual display support. It is currently just a passthrough.
+/* This DisplaySurface implementation supports virtual displays, where GLES
+ * and/or HWC compose into a buffer that is then passed to an arbitrary
+ * consumer (the sink) running in another process.
+ *
+ * The simplest case is when the virtual display will never use the h/w
+ * composer -- either the h/w composer doesn't support writing to buffers, or
+ * there are more virtual displays than it supports simultaneously. In this
+ * case, the GLES driver works directly with the output buffer queue, and
+ * calls to the VirtualDisplay from SurfaceFlinger and DisplayHardware do
+ * nothing.
+ *
+ * If h/w composer might be used, then each frame will fall into one of three
+ * configurations: GLES-only, HWC-only, and MIXED composition. In all of these,
+ * we must provide a FB target buffer and output buffer for the HWC set() call.
+ *
+ * In GLES-only composition, the GLES driver is given a buffer from the sink to
+ * render into. When the GLES driver queues the buffer to the
+ * VirtualDisplaySurface, the VirtualDisplaySurface holds onto it instead of
+ * immediately queueing it to the sink. The buffer is used as both the FB
+ * target and output buffer for HWC, though on these frames the HWC doesn't
+ * do any work for this display and doesn't write to the output buffer. After
+ * composition is complete, the buffer is queued to the sink.
+ *
+ * In HWC-only composition, the VirtualDisplaySurface dequeues a buffer from
+ * the sink and passes it to HWC as both the FB target buffer and output
+ * buffer. The HWC doesn't need to read from the FB target buffer, but does
+ * write to the output buffer. After composition is complete, the buffer is
+ * queued to the sink.
+ *
+ * On MIXED frames, things become more complicated, since some h/w composer
+ * implementations can't read from and write to the same buffer. This class has
+ * an internal BufferQueue that it uses as a scratch buffer pool. The GLES
+ * driver is given a scratch buffer to render into. When it finishes rendering,
+ * the buffer is queued and then immediately acquired by the
+ * VirtualDisplaySurface. The scratch buffer is then used as the FB target
+ * buffer for HWC, and a separate buffer is dequeued from the sink and used as
+ * the HWC output buffer. When HWC composition is complete, the scratch buffer
+ * is released and the output buffer is queued to the sink.
  */
-class VirtualDisplaySurface : public DisplaySurface {
+class VirtualDisplaySurface : public DisplaySurface,
+                              private BnGraphicBufferProducer,
+                              private ConsumerBase {
 public:
     VirtualDisplaySurface(HWComposer& hwc, int32_t dispId,
             const sp<IGraphicBufferProducer>& sink,
             const String8& name);
 
+    //
+    // DisplaySurface interface
+    //
     virtual sp<IGraphicBufferProducer> getIGraphicBufferProducer() const;
-
+    virtual status_t prepareFrame(CompositionType compositionType);
     virtual status_t compositionComplete();
     virtual status_t advanceFrame();
     virtual void onFrameCommitted();
     virtual void dump(String8& result) const;
 
 private:
+    enum Source {SOURCE_SINK = 0, SOURCE_SCRATCH = 1};
+
     virtual ~VirtualDisplaySurface();
 
-    sp<IGraphicBufferProducer> mSink;
+    //
+    // IGraphicBufferProducer interface, used by the GLES driver.
+    //
+    virtual status_t requestBuffer(int pslot, sp<GraphicBuffer>* outBuf);
+    virtual status_t setBufferCount(int bufferCount);
+    virtual status_t dequeueBuffer(int* pslot, sp<Fence>* fence,
+            uint32_t w, uint32_t h, uint32_t format, uint32_t usage);
+    virtual status_t queueBuffer(int pslot,
+            const QueueBufferInput& input, QueueBufferOutput* output);
+    virtual void cancelBuffer(int pslot, const sp<Fence>& fence);
+    virtual int query(int what, int* value);
+    virtual status_t setSynchronousMode(bool enabled);
+    virtual status_t connect(int api, QueueBufferOutput* output);
+    virtual status_t disconnect(int api);
+
+    //
+    // Utility methods
+    //
+    static Source fbSourceForCompositionType(CompositionType type);
+    status_t dequeueBuffer(Source source, uint32_t format,
+            int* sslot, sp<Fence>* fence);
+    void updateQueueBufferOutput(const QueueBufferOutput& qbo);
+    void resetPerFrameState();
+
+    // Both the sink and scratch buffer pools have their own set of slots
+    // ("source slots", or "sslot"). We have to merge these into the single
+    // set of slots used by the GLES producer ("producer slots" or "pslot") and
+    // internally in the VirtualDisplaySurface. To minimize the number of times
+    // a producer slot switches which source it comes from, we map source slot
+    // numbers to producer slot numbers differently for each source.
+    static int mapSource2ProducerSlot(Source source, int sslot);
+    static int mapProducer2SourceSlot(Source source, int pslot);
+
+    //
+    // Immutable after construction
+    //
+    HWComposer& mHwc;
+    const int32_t mDisplayId;
+    const String8 mDisplayName;
+    sp<IGraphicBufferProducer> mSource[2]; // indexed by SOURCE_*
+
+    //
+    // Inter-frame state
+    //
+
+    // To avoid buffer reallocations, we track the buffer usage requested by
+    // the GLES driver in dequeueBuffer so we can use the same flags on
+    // HWC-only frames.
+    uint32_t mProducerUsage;
+
+    // Since we present a single producer interface to the GLES driver, but
+    // are internally muxing between the sink and scratch producers, we have
+    // to keep track of which source last returned each producer slot from
+    // dequeueBuffer. Each bit in mLastSlotSource corresponds to a producer
+    // slot. Both mProducerSlotSource and mProducerBuffers are indexed by a
+    // "producer slot"; see the mapSlot*() functions.
+    uint32_t mProducerSlotSource;
+    sp<GraphicBuffer> mProducerBuffers[BufferQueue::NUM_BUFFER_SLOTS];
+
+    // The QueueBufferOutput with the latest info from the sink, and with the
+    // transform hint cleared. Since we defer queueBuffer from the GLES driver
+    // to the sink, we have to return the previous version.
+    QueueBufferOutput mQueueBufferOutput;
+
+    //
+    // Intra-frame state
+    //
+
+    // Composition type and GLES buffer source for the current frame.
+    // Valid after prepareFrame(), cleared in onFrameCommitted.
+    CompositionType mCompositionType;
+
+    // Details of the current sink buffer. These become valid when a buffer is
+    // dequeued from the sink, and are used when queueing the buffer.
+    uint32_t mSinkBufferWidth, mSinkBufferHeight;
+
+    // mFbFence is the fence HWC should wait for before reading the framebuffer
+    // target buffer.
+    sp<Fence> mFbFence;
+
+    // Producer slot numbers for the buffers to use for HWC framebuffer target
+    // and output.
+    int mFbProducerSlot;
+    int mOutputProducerSlot;
+
+    // Debug only -- track the sequence of events in each frame so we can make
+    // sure they happen in the order we expect. This class implicitly models
+    // a state machine; this enum/variable makes it explicit.
+    //
+    // +-----------+-------------------+-------------+
+    // | State     | Event             || Next State |
+    // +-----------+-------------------+-------------+
+    // | IDLE      | prepareFrame      || PREPARED   |
+    // | PREPARED  | dequeueBuffer [1] || GLES       |
+    // | PREPARED  | advanceFrame [2]  || HWC        |
+    // | GLES      | queueBuffer       || GLES_DONE  |
+    // | GLES_DONE | advanceFrame      || HWC        |
+    // | HWC       | onFrameCommitted  || IDLE       |
+    // +-----------+-------------------++------------+
+    // [1] COMPOSITION_GLES and COMPOSITION_MIXED frames.
+    // [2] COMPOSITION_HWC frames.
+    //
+    enum DbgState {
+        // no buffer dequeued, don't know anything about the next frame
+        DBG_STATE_IDLE,
+        // no buffer dequeued, but we know the buffer source for the frame
+        DBG_STATE_PREPARED,
+        // GLES driver has a buffer dequeued
+        DBG_STATE_GLES,
+        // GLES driver has queued the buffer, we haven't sent it to HWC yet
+        DBG_STATE_GLES_DONE,
+        // HWC has the buffer for this frame
+        DBG_STATE_HWC,
+    };
+    DbgState mDbgState;
+    CompositionType mDbgLastCompositionType;
+
+    const char* dbgStateStr() const;
+    static const char* dbgSourceStr(Source s);
 };
 
 // ---------------------------------------------------------------------------